Getter pump module and system

ABSTRACT

A getter pump module includes a number of getter disks provided with axial holes, and a heating element which extends through the holes to support and heat the getter disks. The getter disks are preferably solid, porous, sintered getter disks that are provided with a titanium hub that engages the heating element. A thermally isolating shield is provided to shield the getter disks from heat sources and heat sinks within the chamber, and to aid in the rapid regeneration of the getter disks. In certain embodiments of the present invention the heat shields are fixed, and in other embodiments the heat shield is movable. In one embodiment, a focus shield is provided to reflect thermal energy to the getter material from an external heater element and provide high pumping speeds. An embodiment of the present invention also provides for a rotating getter element to enhance getter material utilization.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/015,466, filed Apr. 15, 1996, and is a continuation-in-part of U.S.patent application Ser. Nos. 08/332,564, filed Oct. 31, 1994, U.S. Pat.No. 5,685,963; 08/348,798, filed Dec. 2, 1994, U.S. Pat. No. 5,911,560;and 08/521,943, filed Sep. 1, 1995, U.S. Pat. No. 5,972,183; thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to ultra-high vacuum systems, and, moreparticularly, to in situ getter pumps used in semiconductormanufacturing systems.

There are a number of processes which require ultra-high vacuum levelsof, for example, 10⁻⁷ to 10⁻¹² Torr. For example, high vacuum physicsmachines such as cyclotrons and linear accelerators often require avacuum of the order of 10⁻⁸ -10⁻¹² Torr. Also, in the semiconductormanufacturing industry, ultra-high vacuums of approximately 10⁻⁷ -10⁻⁹Torr are often required in semiconductor processing equipment.

Several pumps are often used in series or parallel to achieve ultra-highvacuum levels within a chamber. A mechanical (e.g. oil) pump is oftenused to reduce the pressure within a chamber to approximately 30-50millitorr. These are often referred to as "high pressure" pumps sincethey only pump relatively high pressure gasses. Then, a high- orultra-high vacuum pump, such as a molecular pump, cryopump, turbo pump,or the like, is used to reduce the pressure to approximately 10⁻⁷ -10⁻⁹Torr. These are often referred to as "low pressure" pumps since theypump low pressure gasses. The pump-down time for a particular chambercan range from minutes to hours to days depending upon such factors asthe size of the chamber, the capacity of the pumps, the conductance fromthe chamber to the pumps, and the desired final pressure.

In certain ultra-high vacuum applications, getter pumps have been usedin conjunction with the aforementioned mechanical, molecular, andcryopumps. A getter pump includes getter materials comprising metals ormetal alloys which have an affinity for certain non-noble gases. Forexample, depending upon the composition and temperature of the gettermaterial, getter pumps have been designed which preferentially pumpcertain non-noble gases such as water vapor and hydrogen.

For example, getter pumps provided by SAES Getters, S.p.A. of Milan,Italy, typically include getter material encased in a stainless steelcontainer. Getter pumps can operate from ambient temperatures to about450° C., depending upon on the species of gas to be pumped, the gettercomposition, etc. A preferred getter material for prior art SAES getterpumps is St 707 getter material (which is an alloy of Zr-V-Fe) and whichis produced by SAES Getters, S.p.A. of Milan, Italy. Another suchmaterial is St 101™ getter alloy, also available from SAES Getters,S.p.A., which is an alloy of Zr--Al. Some of these prior art getterpumps can be considered in situ pumps in that they are disposed withinthe high vacuum physics machines.

Some present getter pump designs employ getter devices comprising metalribbons coated with a powdered getter material such as the St 707 and St101™ getter alloys just described. The coated ribbons are pleated in aconcertina fashion to increase the ratio of exposed surface area to thevolume occupied by the coated ribbon, and to increase adsorption ofdesired gasses. Such pumps are manufactured by SAES Getters, S.p.A., andsold under the trade name SORB-AC®. In addition, recent designs haveemployed disk-shaped substrates coated with getter material powders.Designs using coated substrates have a drawback in that the total amountof getter material available for sorption is limited to the nominalsurface area of the getter device substrate.

It is has been suggested that getter pumps be provided for semiconductorprocessing equipment. For example, in an article entitled"Non-Evaporable Getter Pumps for Semiconductor Processing Equipment" byBriesacher, et al., and published in Ultra Clean Technology 1(1):49-57(1990), it is suggested that any application which uses getters topurify processed gases for semiconductor processing can also utilizenon-evaporable getter pumps for in situ purification and for theselective pumping of impurities.

The aforementioned Briesacher reference discloses that there are twopossible operating scenarios for the use of getter pumps in a sputteringsystem, which is a type of semiconductor processing equipment. The firstis the addition of the getter pump to the system to operate in parallelwith conventional pumps (e.g. mechanical and cryopumps) of the system.In this scenario, the operation of the system is not modified in anyway, and the getter pump merely serves as an auxiliary pump to lower thepartial gas pressure of certain components of the residual gas in thechamber. The second scenario requires filling the chamber to a pressurein the range of 3×10⁻³ to 6×10⁻³ Torr, stopping the argon flow into thechamber, and sealing the chamber. The getter pump is then said to act asan "in situ" purifier for the argon. However, as discussed below, thepump is not truly "in situ" in that the active material is not withinthe volume of the processing chamber.

In a typical sputtering system, a noble gas (usually argon) is pumpedinto a chamber and a plasma is created. The plasma acceleratespositively charged argon ions towards a negatively charged target,thereby causing material to become dislodged and to settle on thesurface of the wafer. Getter pumps are well adapted for use withsputtering systems, since the only desired processing gas is a noble gaswhich is not pumped by the getter pump. Therefore, the getter pump canremove impurity gases from a sputtering chamber without affecting theflow of the noble gas required for the sputtering process.

The Briesacher reference was primarily an academic analysis of thepracticality of using non-evaporable getter pumps in semiconductorprocessing equipment. Therefore, very little practical application ofthe theory is disclosed. Furthermore, while the Briesacher article usesthe term "in situ" to describe a scenario for the use of a getter pump,it is clear from the description that the getter pump is external to thechamber and is considered "in situ" only in the sense that when thechamber is sealed and when no argon is flowing into the chamber, thevolume within the getter pump can be considered to be connected to thechamber volume. According to the analysis presented by Briesacher, avalve must be placed between the getter containment vessel and the mainchamber to protect the getter from atmospheric exposure that woulddeteriorate the getter and require additional regenerations. Suchprotection is imperative with the strip-type getters discussed in theBriesacher reference. Thus, the getter described by Briesacher is nottruly "in situ" in that the getter pump surfaces are within a volumethat is connected to the chamber volume through a restrictive throat,which greatly limits the conductance between the chamber and the pump.By "conductance" it is meant herein the ease with which a fluid (gas inthis instance) flows from one volume (e.g. the processing chamber) toanother volume (e.g. the pump chamber). Conductance is limited by theaperture size between the two chambers, which is typically thecross-sectional area of the throat of the cryopump.

SUMMARY OF THE INVENTION

The present invention provides an improved getter pump module and systemthat is particularly well adapted for in situ pumping of semiconductorprocessing chambers.

In one preferred embodiment, the present invention includes getter pumpshaving a plurality of getter elements, the getter elements comprisingporous, sintered getter material having an aperture extendingtherethrough and a support element extending through the aperture.Titanium or other metal hubs are typically provided in the apertures ofthe getter elements to provide mechanical support for the getterelements and to enhance thermal transfer between the heating element andthe getter elements. The getter elements, which are typically diskshaped, are preferably partially surrounded by a shield which providesthermal isolation between the getter elements and other devices andsurfaces within a semiconductor processing chamber, and which also aidsin the getter element regeneration process.

In a preferred embodiment, a radiative heater is used to heat the gettermaterial. In another preferred embodiment, the present inventionincludes getter pumps in which the faces of adjacent getter elements arenot parallel, which getter elements include apertures through which aheating element is extended. In preferred embodiments, the aperturesdefine an axis and the getter elements are arranged at angles notperpendicular to the axis. In another embodiment, the apertures aresubstantially perpendicular to the axis, but the faces of adjacentgetter elements are inclined with respect to each other, preferably atequal and opposite angles.

In still another embodiment, the present invention includes asemiconductor processing system comprising a processing chamber, an insitu getter pump having a plurality of getter elements, each having anaperture extending therethrough, and a support element extending throughthe aperture. The getter pump has an actual pumping speed with respectto the processing chamber which is at least 75% of the theoreticalpumping speed of the plurality of getter elements in an unlimitedvolume.

The present invention also includes a method for processing a waferwhich includes the steps of (a) placing a wafer within a processingchamber, the chamber including an in situ getter pump having aconductance of greater than about 75% disposed within the waferprocessing chamber, the in situ getter pump including a plurality ofgetter elements; (b) sealing the chamber; (c) flowing a noble gas intothe chamber while simultaneously pumping the chamber with an externallow pressure pump and the in situ getter pump, the low pressure pumpoperative to remove noble gasses from the chamber and which in situgetter pump operative to remove non-noble gasses from the chamber; and(d) processing the wafer in the chamber while flowing the noble gas intothe chamber. The present invention also includes the wafer produced bythe method of the invention.

In yet another embodiment, the present invention includes a method forpumping a chamber, which includes the steps of (a) sealing the chamberfrom the external atmosphere; and (b) pumping the chamber with an insitu getter pump disposed within the chamber, the in situ getter pumphaving a conductance of greater than about 75% and the in situ getterpump being capable of operating at more than one temperature to pumpthereby selected non-noble gasses at different getter temperatures.

In a still yet another embodiment, the present invention provides agetter pump which pump includes porous, sintered getter material and aheater which is proximate to the getter material to heat the gettermaterial. The heater is also proximate to a focus shield that reflectsthermal energy emitted by the heater onto the getter material. Thegetter pump has a conductance of at least about 75% with respect to aproximate volume to be pumped. This embodiment can further include athermally isolating wall upon which wall the getter material and heaterare supported. The thermally isolating wall can also be part of an"L-shaped shield" and may further include a thermally reflectivesurface.

Additional aspects and advantages of the invention will become moreapparent when the following description is read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation of a semiconductor processingsystem, including an in situ getter pump module of the presentinvention.

FIG. 2 is a partial perspective view a number of getter elements of theinvention and a thermally isolating shield.

FIG. 3 is a facing view of a getter element of FIG. 2.

FIGS. 4A and 4B illustrate sectional views of getter elements of theinvention. FIG. 4A is a sectional view of a single getter element takenalong the line 4A--4A of FIG. 3. FIG. 4B is a sectional view of threeabutting getter elements, also along taken the line 4A--4A of FIG. 3.

FIG. 5 is an illustration of the number of collisions between a moleculeand two adjacent getter elements of the invention as a function of thedistance between the getter elements.

FIGS. 6A and 6B illustrate certain dimensional parameters of the getterelements of the invention. FIG. 6A illustrates dimensional parameters ofadjacent getter elements in a arcuate configuration. FIG. 6B illustratesdimensional parameters for adjacent parallel getter elements.

FIG. 7 is a graphical representation of the relationship between pumpingspeed and the distance "d" between adjacent getter elements.

FIG. 8 is an illustration of another embodiment of the invention whereinadjacent getter elements are arranged at opposing angles.

FIG. 9 is an illustration of yet another embodiment of the inventionwherein the facing sides of adjacent getter elements are non-parallel.

FIG. 10 illustrates an embodiment of the invention wherein an array ofgetter elements is arranged partially circumferentially around asputtering platter.

FIG. 11 is an illustration of an embodiment of the invention whereinstar-shaped arrays of getter elements are supported on a rotatingsupport element.

FIG. 12 is a side view of the embodiment shown in FIG. 11, but whereinthe getter elements are inside a thermally isolating shield.

FIG. 13 is a side view of the embodiment illustrated in FIG. 2, butwherein the getter elements are inside a thermally isolating shield.

FIGS. 14A and 14B illustrate a side view of a thermally isolating shieldof the invention which moves between open and closed configurations.FIG. 14A illustrates a closed configuration in which the getter elementsare thermally isolated. FIG. 14B is an illustration of an openconfiguration in which the getter elements are exposed to thesurrounding environment.

FIG. 15 is a partial cut-away view of the embodiments shown in FIGS. 14Aand 14B, further showing gas sources.

FIG. 16 is an illustration of a getter pump that includes a focusshield.

FIG. 17 is a cut-away view of the embodiment illustrated in FIG. 16,further including an L-shaped thermally isolating shield.

FIG. 18 is an illustration of one embodiment of the getter pump of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a portion of a semiconductor processing system 100 inaccordance with the present invention. The processing system includes awafer processing chamber 102 having an interior wall 103. An externalpump 104 ("P"), such as a cryopump and/or a mechanical pump, is coupledto the chamber by a conduit 105 to reduce the internal atmosphericpressure of the chamber before the getter pump module is operated.Preferably, the internal pressure of the chamber is brought to a levelof about 10⁻⁶ bar before the getter pump is activated. Inside chamber102 is included a sputtering stage 106 which includes a chuck 108 thatrests atop a support 110. Also included are heat lamps 112 and 112' andat least one in situ getter pump module such as shown generally at 114and 116. Chamber 102 typically is one component of a multi-componentsemiconductor processing system which includes, inter alia, variouspower sources, analyzers, cryopumps, plasma generators, low vacuumpumps, high vacuum pumps and controllers. These other components,including their design, manufacture and operation, are well known tothose of skill in the art.

As used herein, the phrase "in situ getter pump" will refer to a getterpump where the active elements, i.e. the active getter material, isphysically located within the same volume of space as the wafer beingprocessed. As such, the conductance between the in situ getter materialand the process chamber is very high compared to the coupling of anexternal getter pump to the chamber through a gate valve, conduit, thethroat of a pump, etc. This results in a relatively high pumping speed.For example, with an in situ getter pump of the present invention, morethan 75% of maximum theoretical pumping speed can be achieved, ascompared to at best 75% of maximum theoretical pumping speed for anexternal getter pump coupled to the processing chamber with a gate valveor the like.

The getter pump module 114 and/or 116 is "activated" by heating thegetter material of the getter pump to a high temperature, e.g. 450° C.This activation of the getter pump is required because the gettermaterial becomes "passivated" upon exposure to the atmosphere, and mayoverlap with a "bake-out" step wherein lamps 112 and 112' are used tobake out the chamber to rid the chamber of residual gasses, moisture,etc. However, the bake out period and the activation periods need notcoincide.

With continuing reference to FIG. 1, in situ getter pumps 114 and 116will now be described in greater detail. Pumps 114 and 116 preferablyinclude thermally isolating shields 118 and 126 respectively. Theshields may further include thermally reflective interior walls 120 and128 to enhance the regeneration of the getter elements by reflectingback heat to the getter elements. Within the thermally isolating shieldsare getter assemblies 122 and 130 which are supported on supports showngenerally at 124 and 132. Getter assembly 114 is illustrative of a "lowboy" configuration which may be required due to space limitations withinthe processing chamber. Getter module 126 is an example of a preferred"high boy" configuration which provides a relatively greater conductancebetween the getter assembly 130 and the interior of the processingchamber due to a relatively greater opening than that which is providedby the low boy configuration.

The getter pumps 114 and 116 further include heaters 134 and/or 134',and 136 and/or 136', respectively, for heating the getter material totemperatures effective to "activate" the getter material as describedabove, and/or to control the adsorption characteristics of the gettermaterial as is well known in the art. Heaters 134, 134', 136 and 136'can be resistive heaters, i.e., heaters that use at least in partelectrical resistance for heating, or radiative heaters, i.e., heatersthat employ radiation to effect heating of nearby surfaces. Preferably,heaters 134 and 136 are resistive heaters and are disposed through anaperture in the getter elements as will be described in greater detailbelow. It will be appreciated that heaters 134 and 136 can also fulfilla support function, supporting the getter elements in addition toheating the getter material. Heater elements 134' and 136' arepreferably radiant heaters and are disposed proximate to the gettermaterial and the walls of the thermally isolating shield. It will beappreciated that heater elements 134' and 136' may be disposed atvarious locations within the thermally isolating shield. Preferredlocations are those from which the heaters can efficiently heat thegetter material to the desired temperatures without affectingsignificantly structures within the processing chamber.

An in situ getter pump in accordance with the present invention isillustrated at 200 in FIG. 2. The pump includes a getter assembly 202and an elongated, box-shaped thermally isolating shield 214 forthermally isolating the getter assembly from the interior of thesemiconductor processing chamber 102. Although the shield 214 ispreferred, it can be eliminated if the getter assemblies are positionedor otherwise shielded from the heated surfaces in the chamber.

Getter assembly 202 includes a plurality of disk-shaped getter elements204, each comprised of getter material 206. The getter elementspreferably include a centrally located aperture 208, through whichaperture extends a support element 210 to physically support theelements. In a preferred embodiment, the aperture is a substantiallycylindrical bore extending through the getter element. Other apertureconfigurations will be recognized to be equivalent. Support element 210can further include a resistive element 212 running through the supportelement to form a resistive heating element to heat to the getterelements to a regeneration temperature in addition to lower temperaturesat which the getter material will remove certain gasses preferentiallyfrom the atmosphere as is well known in the art. The support elementpreferably is of a tubular, cylindrical design formed from stainlesssteel, and is dimensioned to engage with the aperture to providecontact, including thermal contact, with the getter elements. Supportelements are available commercially from various suppliers. Supportelements which are effective to act as heating elements are soldcommercially by Watlow.

In a preferred embodiment, the heating of the getter material isperformed using heater element 210' located proximate to the gettermaterial. Heating element 210' is preferably a radiative heater, e.g., aSylvania quartz infrared lamp such as available commercially fromOsram-Sylvania of Winchester, Ky., USA. Preferably, the heating element210' runs in a direction substantially parallel to the path defined bythe axes of the getter elements, which can be supported by a simple(i.e., unheated) rod, preferably of stainless steel. It will beappreciated that a metal supporting rod can also provide heat to thegetter material by conduction. Other arrangements of the heater andgetter elements will be apparent to those of skill in the art. Forexample, the getter elements may be held in other fashions, such as bytheir edges. The heating element can be a single integral heatingelement, as shown in FIG. 2, or it can comprise a series of discreteheating elements.

The thermally isolating shield 214 comprises an exterior surface 216which is effective to block radiant heat from the external heat sourceswithin the chamber from affecting the getter elements. The shield mayalso include a thermally reflective interior surface 218 facing thegetter elements which functions to increase regeneration efficiency byreflecting heat back onto the getter assemblies during theirregeneration. In addition, the interior surface of the shield can alsoserve to prevent heat from the regeneration of the getter elements fromreaching surfaces within the chamber outside of the thermally isolatingshield 214. In a preferred embodiment, the shields are made from 316Stainless Steel which as been electropolished to about 25 RA.

A preferred embodiment of a single getter element is shown in FIG. 3 at300. This preferred getter element comprises a solid, porous, sintereddisk of getter material 302 which disk includes a non-getter metallichub 304 disposed within the aperture of the disk and a non-gettermetallic spacer 306. The spacer and hub define an aperture 308 which ispreferably cylindrical and dimensioned to receivably engage thesupport/heating element. In preferred embodiments, both the hub andspacer are made from titanium. As used herein, the term "disk" refers toa getter element having a substantially circular or ovoid outerperiphery and a surface area in excess of its thickness. Although asubstantially planar getter element is preferred for reasons which willbecome apparent below, deviation from planarity is also encompassed bythe present invention.

By "solid" it is meant that the getter material comprises the body ofthe getter element, such as described in U.S. Pat. No. 5,320,496 toManini, et al., entitled "High-Capacity Getter Pump", and which isincorporated herein by reference, as opposed to other getter elementswherein getter material is adhered to a substrate surface. By providinga solid, porous getter disk, pumping efficiency and impurity capacity isgreatly increased since molecules can be adsorbed deep into the body ofthe getter element, rather just on the surface as with prior art getterelements.

The getter elements can be made from a variety of getter materials,depending upon their desired properties. Typical getter materialsinclude alloys of zirconium, vanadium and iron as disclosed in U.S. Pat.Nos. 3,203,901, 3,820,919, 3,926,832, 4,071,335; 4,269,624, 4,428,856,4,306,887, 4,312,669, 4,405,487, 4,907,948 and 5,242,559; and BritishPatent No. 1,329,628 and British Patent Application No. GB 2,077,487A;and German Patent No. 2,204,714, each of which is incorporated herein byreference. Additional types of getter materials include, among others,titanium, hafnium, uranium, thorium, tungsten, tantalum, niobium, carbonand alloys thereof.

A preferred getter material comprises a zirconium-vanadium-iron ternaryalloy having a weight composition such that the percentages of weightsof the three metals, when plotted on a ternary composition diagram fallwithin a triangle whose vertices lie at a) 75% Zr/20% V/5% Fe; b) 45%Zr/20% V/35% Fe; and c) 45% Zr/50% V/5% Fe. More preferably, the gettermaterial comprises a ternary alloy having a composition of 70% Zr/24.6%V/5.4% Fe by weight, which ternary alloy is sold under as St 707 by SAESGETTERS, S.p.A. Such materials are described in U.S. Pat. No. 4,312,669and British Patent Application No. GB 2,077,487A.

Another preferred getter alloy is one made from zirconium and aluminum,comprising about 84% zirconium by weight and 16% aluminum by weight.Such material is sold under the trade name St 101® by SAES GettersS.p.A. Still another preferred getter material comprises 17% carbon and83% zirconium by weight and is sold under the trade name St 171® by SAESGetters S.p.A. Yet another preferred getter material comprises 82%zirconium, 14.8% vanadium and 3.2% iron by weight and is sold under thetradename St 172 by SAES Getters S.p.A. Another preferred gettermaterial comprises 10% molybdenum, 80% titanium and 10% titanium hydride(TiH₂) by weight and is sold under the tradename St 175 by SAES GettersS.p.A. Those of skill in the art will appreciate that these gettermaterials can be prepared by analogy to the descriptions in theabove-cited patents and patent applications.

Highly porous getter materials tend to be preferable to less porousmaterials in that they tend to have higher adsorption capabilities. Suchporous getter materials can be prepared in accordance with thedescriptions in U.S. Pat. No. 4,428,856, which describes the preparationof porous getter bodies from a mixture of powders including titanium,titanium hydride and a refractory metal chosen from the group consistingof tungsten, molybdenum, niobium and tantalum; British PatentApplication No. GB 2,077,487A, which describes the preparation of porousgetter material from a mixture of zirconium and the above-describedternary alloy; and German Patent No. 2,204,714 which describes thepreparation of a porous getter material comprising a mixture ofzirconium and graphite powders.

Preferred getter materials and their preparation are described inBritish Patent Application No. GB 2,077,487A. The preferred gettermaterials comprise mixtures of zirconium powder with the above-describedternary alloy in a ratio of between 4 parts zirconium to 1 part ternaryalloy and 1 part zirconium to 6 parts ternary alloy by weight. Morepreferably, the zirconium:ternary alloy ratio is between 2:1 and 1:2.The ternary alloy can be formed, for example, by combing zirconiumsponge with commercially available iron-vanadium alloy (Murex, UnitedKingdom) in a fusion furnace under reduced pressure until molten,cooling the molten material, and milling the resulting solid to apowder.

Formation of the getter elements can be accomplished using a processwhich comprises placing a hub (described below) into a getter elementmold, adding the alloy and the zirconium powders and sintering thematerial at a temperature between about 1000° C. and 1,100° C. for aperiod of between about 5 minutes and about 10 minutes.

FIG. 4A shows a cross section of the getter element shown in FIG. 3taken along the line 4A--4A at 400. As shown in FIG. 4A, the getterelement includes a porous sintered disk of getter material 402 whichdisk includes a hub 404 of non-getter material disposed in an aperturewithin the disk. The hub includes a foot 406 and a central aperture 408.Preferably, the foot of the hub is substantially flush with the disksurface while the opposite end of the hub extends above the surface ofthe disk. However, it will be appreciated that either or both ends ofthe hub may extend above the disk.

The diameter of a preferred getter element of the present invention isabout 25.4 millimeters (mm). The thickness of the getter disk is about1.3 mm. A preferred hub embodiment includes a substantially circularfoot having a diameter of about 8.0 mm, and a foot height of about 0.3mm; and a substantially circular raised portion extending from the foot,the raised portion having a diameter of about 6.0 mm and a height ofabout 1.7 mm (i.e., the total height of the hub is about 2.0 mm). Thus,in is preferred embodiment the raised portion extends above the gettermaterial at a height of about 0.7 mm from the disk surface. The diameterof the aperture extending through the hub that receives the heatingelement or support is about 3.8 mm.

In preferred embodiments, getter pumps are constructed from a pluralityof getter disks which are placed adjacent each other along the axesdefined by the disks' apertures. Such an embodiment is illustrated inFIG. 4B at 450. As shown in FIG. 4B, the getter elements includes afirst disk 452, a second disk 454, and a third disk 456. Each disk isaligned such that a central aperture 458 is formed by the apertures ofthe individual disks. In order to maximize the available surface area,it is preferable to stack the disks such that the hub of any one disk issubstantially touching the spacer of an adjacent disk. Thus, hub 460 ofdisk 452 is shown in contact with spacer 462 of disk 454, and hub 464 ofdisk 454 is in contact with spacer 466 of disk 456. It will beappreciated that the spacers provide gaps through which the gettermaterials can interact with the atmosphere to which the getter pump isexposed. Such gaps are illustrated at 472 and 472', which are formed byopposing faces 476 and 478; and gaps 474 and 474', which are formed byopposing faces 480 and 482. As shown in the Figure, faces 484 and 486 ofthe getter elements at the ends of the stack are free. Typically,however, there will be many getter elements stacked to provide many ofsuch gaps.

Referring to FIG. 5, the parameters required for optimal pumpingfunction will be discussed. As it is well known in the art, theefficiency of a getter pump is related to the distance between thegetter elements. If the getter elements are spaced too widely, gasmolecules will pass between the walls after a few, or no collisions withthe getter material. This is illustrated at 500 where adjacent getterelements 502 and 504 are spaced at a distance which allows molecule 506to collide with either opposing face of the getter elements only a fewtimes along path 508 before passing between the disks without beingadsorbed. Conversely, as the getter elements are brought together, morecollisions between the molecule and the getter element surfaces occur,thereby increasing the likelihood that the molecule will be trapped bythe getter material. This is illustrated at 510 where opposing getterelements 512 and 514 are spaced close enough that molecule 516 collidesseveral times along the opposing getter element faces along path 518.Each time the molecule collides with a getter element surface, there isa certain probability that the molecule will stick to the surface andbecome absorbed therein. Thus, a greater number of collisions betweenthe molecule and the surface will yield a correspondingly greaterlikelihood that the molecule will be trapped by the surface. However, ifthe getter elements are placed too close together (e.g., if they abuteach other), the edge area of the disk will become the dominant pumpingsurface, which is less effective than the facing surfaces of the disks.

In view of the foregoing, preferred getter element designs will takeadvantage of the above-described properties to optimize the efficiencyof the getter pump by employing various geometries, see, e.g.,WO94/02957, published Feb. 3, 1994, to Ferrario, et al., and TechnicalPaper TP 202, American Vacuum Society 39th National Symposium (1992),both of which are incorporated herein by reference. The relevantparameters to be considered are shown in FIG. 6A by reference toopposing disks 602 and 604. The relevant parameters include the diskradius "D," inter-element spacing "d" and disk thickness "t." In someembodiments, the getter elements will be arranged in a fan pattern suchas that shown at 610 in FIG. 6B. There, disks 612, 614, and 616 arearranged in an arcuate pattern having an angle "α" between the disks.Thus, the inter-element spacing d will be related to the angle α and thelength I of the getter element.

The above-described relationship between the arrangement and dimensionsof the getter elements and the efficiency of the getter pump isillustrated in FIG. 7 along path 700, which shows the relationshipbetween pumping speed "S" and the inter-element distance "d" asdetermined by experimental tests of disk performance as a function ofthe above-described parameters. As seen in FIG. 7, when the getterelements are touching, i.e., when d=0, the pumping speed is at the value"S₁." As the inter-element spacing increases, the pumping speedincreases until reaching a maximum at which point further increases inthe distance between getter elements allow fewer molecular reflectionsbetween the disks; thereby increasing the probability that the moleculewill fly between the surfaces of the disks. By extending the distancebetween adjacent getter elements sufficiently, the pumping speed can bedecreased below that for the case where all of the getter elements aretouching. The optimum parameters for disk spacing can be determined byplotting the pumping speed versus the disk spacing and finding themaximum of the resulting distribution. For the aforementioned 25.0 mmdiameter disk shaped getter elements, a spacing of about 0.7 mm ispreferred for pumping H₂, a common impurity gas in semiconductorprocessing operations. It will be appreciated that other disk spacingsmay be preferred for pumping impurity gases other than H₂.

A preferred embodiment employing the above-described relationshipbetween getter element spacing and pumping speed is illustrated in FIG.8 at 800. There, the opposing faces of the adjacent getter elements arenot parallel with respect to each other, relative to the axes defined bythe apertures of elements 804, which apertures are aligned along an axisthat is parallel to heating element 802. As will be appreciated from theillustration, the axes of elements 804 are arranged such that thesurface planes 806 and 808 are not perpendicular to the axis defined bythe apertures. In a preferred embodiment, the apertures of the adjacentgetter elements are inclined along the axis at opposing angles, thusallowing adjacent getter elements to form a partial "V" shape.

FIG. 9 shows an alternative embodiment wherein adjacent getter elements902 include hubs 904 having apertures that are substantiallyperpendicular to their common axis. In this embodiment, the faces of theadjacent getter elements are inclined relative to the axis formed bytheir apertures. In preferred embodiments, the opposing faces of thegetter elements, shown generally at 908 and 910, are inclined relativeto the axis and at opposing angles. Such an arrangement provides for asteady narrowing of the inter-element distance proceeding from theperipheral edges of the getter elements toward their hubs. Preferredangles and distances are described in Briesacher, et al., Ultra CleanTechnology 1(1):49-57 (1990), which is incorporated herein by reference.

Certain embodiments of the invention include straight and curved getterpump segments to accommodate the space restrictions inherent insemiconductor processing chambers. As shown in FIG. 10 at 1000, aprocessing chamber having a wall 1002, heat lamps 1006 and 1008, and asputtering stage 1004, includes a getter pump 1010 having getterelements 1012 supported on heating element 1014. The getter pumpincludes curved portions 1018 and straight portions 1020 which allowplacement of the getter pump in close proximity to the sputter stage1004. It will be appreciated by those of skill in the art thatmaintaining close proximity of the getter pump to the stage facilitatesthe pumping of non-noble gasses to produce a low-impurity partialpressure where such a partial pressure is most important--near the waferbeing processed.

It will be further appreciated by those skilled in the art that theplacement of the getters within an elongate, box-shaped shield structuresuch as shown in FIG. 2 can provide uneven exposure of the getterelements, with those portions of the getter elements closer to theaperture receiving greater exposure to the chamber atmosphere than thoseportions of the getter elements closer to the interior of the shields.Such an arrangement therefore could underutilize the sorptive capacityof the getter elements.

An embodiment of the getter segments of the present invention that wouldsubstantially avoid this potential problem is illustrated in FIG. 11 at1100. There, a shaft 1102 of a motor 1106 is coupled to a magneticcoupling device 1128 disposed on the outer side of a chamber wall 1105.A second magnetic coupling device 1110 is disposed on the other (inner)side of the chamber wall 1105. The magnetic coupling device 1110 iscoupled to the support/heater element 1126 by a connector 1112.Optionally a heater element (not shown) external to the getter elementsmay be used with support/heater element 1126.

In this alternate embodiment, getter pump module 1107 comprises aplurality of star-shaped getter assemblies 1114, which assemblies eachinclude a hub having a centrally located aperture and a plurality ofgetter elements 1116, 1118, 1120, 1122 and 1124 extending radially fromthe hub. The getter elements in this particular embodiment of theinvention are substantially paddle shaped, i.e., the getter elementshave a substantially rectangular or fan shaped cross section along anaxis which is longer than the width or depth of the getter element. Thegetter assemblies are supported by a heating element 1126 which rotatesin the direction indicated.

Those skilled in the art will appreciate that such an embodiment willincrease the utilization of the capacity of the getter elements, asillustrated in FIG. 12 at 1200, where rotating getter pump 1202 isplaced inside shield 1204. As the Figure illustrates, getter elements1207 are in close proximity to the aperture of shield 1204, therebyreceiving greater exposure to the chamber atmosphere relative to getterelements 1208 which are in close proximity to the interior shield wall1206. Rotation about central hub 1210 using motor 1212 allows the lesserexposed getter elements 1208 to be moved forward toward the aperturewhile the more exposed getter elements 1207 are moved toward the rear ofthe shield. Thus, the exposure across all of the getter elements is moreuniform.

Referring back to FIG. 2, it will be noted that in preferredembodiments, a thermally isolating shield is provided to isolatethermally the getter pump from the processing chamber. Such isolating isadvantageous as it protects the getter elements from the effects of theheat lamps that are used to "bake-off" residual gases from the surfacesof the walls and other components in the processing chamber, and,conversely, to protect the components in the chamber from heat releasedfrom the getter pump during regeneration of the getter elements.

Referring now to FIG. 13, a thermally shielded getter pump isillustrated at 1300. The shielded getter pump includes a box-likethermally isolating shield 1302 shielding getter elements 1304, whichgetter elements are supported by a support 1314. The thermally isolatingshield preferably comprises an outer surface 1306 and a thermallyreflective inner surface 1308 which inner surface faces the getterelements 1304. In preferred embodiments, the thermally isolating shieldincludes a floor shown generally at 1312. The thermally isolating shieldwill include an aperture such as shown at 1316 to allow contact betweenthe atmosphere in the processing chamber and the getter elements. Theshields are preferably made from a suitably thermally reflectivematerial, such as, but not limited to, "316 Stainless Steel", and theinterior surface of the shields may be coated or plated (such as withnickel) to enhance reflectivity. Alternatively, the shield may bepolished or electropolished to enhance reflectivity, reduce porosity(which reduces gas and moisture adsorption), and minimize particulatecontamination. Within central hub 1320 is disposed support/heaterelement 1322. Optionally, an external heater 1322' can be used.

In some embodiments, the thermally isolating shield is an elongate,stationary box shaped structure which may be fixed to one or moresurfaces of the chamber interior. In some embodiments, the getterelements will be spaced relatively uniformly between the top, sides andbottom of the thermally isolating shield. Such an embodiment is commonlyreferred to as the aforementioned "low boy" structure. In otherembodiments, the spacing between the getter elements and the floor ofthe thermally isolating structure is larger than the spacing between thegetter elements and the remaining sides of the thermally isolatingshield. Such embodiments are typically referred to as the aforementioned"high boy" structure. These embodiments are denoted in FIG. 13 by theparameter "1". Preferably, 1 is about 0 mm for the "low boy"configuration and between about 13 mm and about 25 mm for the "high boy"configuration.

A second shield embodiment including a moveable shield is illustrated inFIGS. 14A and 14B. Such a moveable shield minimizes conductance loss byallowing substantially all of the getter elements to be exposed to thechamber atmosphere simultaneously, and yet can isolate the getterelements as desired for regeneration, system maintenance, duringbake-out, etc. As illustrated in FIG. 14A of 1400, a moveable shieldembodiment wherein the shield is in a closed position, i.e., all of theshield elements 1402, 1404 and 1406 are covering the getter elements, isdescribed. The shield elements rotate about hub 1408 which hub issupported by support 1410. The movable shield elements are, again,preferably made from stainless steel.

FIG. 14B illustrates an open position of the shield at 1420 in whichgetter element 1422 is exposed substantially to the chamber atmosphere.The mechanism for opening and closing the shield is also illustrated. Ina preferred embodiment, the mechanism for opening and closing the shieldcomprises a flexible tube 1424 which tube includes a ring 1426 coupledto a one way valve 1428. The ring is further pivotably coupled to theproximal end of a rod 1429, which rod is slideably coupled to thegrooved extension of a gear 1430 which extension slideably receives thedistal end of the rod. The geared portion of gear 1430 is engaged with asmaller gear (not shown) which smaller gear is coupled to the shields1402, 1404 and 1406. When the tube is charged with gas and straightens,the rising of collar 1426 causes a rotation of gear 1430 which in turninitiates a larger rotation in the smaller gear thereby creating arotation of the shields about hub 1408 to a closed position. Conversely,when the tube is discharged and assumes its deflated position, thelowering of ring 1426 causes a rotation of the gears in the reversedirection, opening the shields. In this fashion, the shielded getterpump can be opened and closed remotely. However, it will be appreciatedthat various mechanical, electrical, hydraulic and/or pneumaticmechanisms can be adapted to achieve the same result.

Another view of the embodiment just described is illustrated in FIG. 15at 1500 which shows the shielded getter pump 1502 and the getterelements 1506 and heating element 1508 in a partial cut away at 1504.The shield elements are shown at 1510 and 1512. A gas supply foroperating the mechanism for opening and closing the shield is shown at1512. A second, optional, gas supply (preferably nitrogen) for providinga positive pressure relative to the chamber's atmospheric pressure of agas is also shown at 1514. Preferably, the gasses supplied to the getterpump are inert gasses or nitrogen. In this fashion, the movable shieldcan be closed and a nitrogen purge will isolate the getter elements fromthe ambient environment. Nitrogen is also a preferred gas for providinga "passivating layer" over the getter element surfaces to protect thegetter elements from more harmful gasses, such as oxygen, as thenitrogen layer can be readily removed from the elements by heating(i.e., regeneration). This is particularly useful during systemmaintenance or repair where the chamber is open to the atmosphere, sinceprotecting the getter elements will enhance their useful life spans.

Still another embodiment of the present invention is illustrated at 1600in FIG. 16. There, getter assemblies 1602 and 1604, comprising aplurality of getter disks 1606, each including a hub such as that shownat 1608, are arranged above and below a proximate heater element 1610.The getter assemblies, their constituent getter disks and the heaterelement are substantially as described with respect to FIG. 2 above. Thesupports for getter assemblies 1602 and 1604, and heater element 1610,are not shown.

Next to the getter assemblies and heater element is a focus shield unit1612 which comprises support elements 1614, 1616, and 1618 that togethersupport a focus shield 1620. The focus shield unit is formed from thesame materials described above with respect to thermally isolatingshield 214. Focus shield 1620 comprises a thermally reflective surfacethat is arranged adjacent heater element 1610 and is dimensioned toreflect the heat emitted by the heater element onto the getter disks ofthe getter assemblies 1602 and 1604. In one embodiment, the focus shieldunit comprises a stainless steel material, such as "316 StainlessSteel". The focus shield may also be plated with a highly reflectivematerial (e.g., nickel) and electropolished to about 25 RA.

The focus shield can be a substantially planar, rectangular surface orit can be formed into any configuration that increases the efficiency ofheat transfer from the heater element to the getter disks. For example,the focus shield can be partially or wholly convex, or faceted, with theconvex side of the focus shield directed towards the heater element andgetter disks to enhance the heating of the getter material foractivation. It will be appreciated from the foregoing discussionregarding conductance and exposure that the embodiment shown in FIG. 16has the advantage of providing high conductance--as much as 80% or90%--due to the relatively open construction of the focus shield unit;yet, the arrangement of the focus shield near the heater element and thegetter disks provides sufficient transfer of heat energy to the disks toallow efficient activation of the getter material.

In addition to the particular embodiment shown in FIG. 16, otherembodiments employing the focus shield unit shown in FIG. 16 areincluded in the present invention. In one embodiment, the getterassemblies and heater element are positioned between two focus shieldunits in a substantially symmetric fashion to increase the amount ofheat energy reflected to the getter material. This "symmetric"embodiment can be extended to produce "banks" of getters pumps in whichfocus shield units are arranged in a back-to-back fashion with thegetter assemblies and heater elements being arranged between opposingfocus shield faces. Alternatively, several getter assemblies and heaterelements can be stacked in alternating order with stacked focus shieldsbeing deployed substantially opposite the heater elements. Such anembodiment can be useful where horizontal space is limited, but verticalspace is available. Still more useful arrangements will be apparent tothose having skill in the art.

The focus shield unit of the present invention can also be employedadvantageously in embodiments in which the getter assemblies and heaterelement require greater exposure to the atmosphere of the processingchamber than available using thermally isolating shield other than thatshown in FIG. 2 at 214 (and, hence, provide higher pumping speeds). Onesuch embodiment is illustrated in FIG. 17 at 1700. There, asubstantially "L-shaped" shield 1701, comprising a thermally isolatingwall 1702 and a thermally isolating floor 1703, is provided from whichgetter assemblies 1602 and 1604, and heater element 1610, are suspendedby supports 1704, 1706, and 1708, respectively. Focus shield unit 1612is arranged such that the reflective surface of focus shield 1620 issubstantially opposite heater element 1610, thereby reflecting heatenergy emitted by the heater element to the getter material of thegetter assemblies 1602 and 1604. However, the wall of the L-shield 1702prevents substantial heat transfer to the remainder of the processingchamber and can serve as a reflector to reflect heat energy emitted fromthe heater element to the sides of the getter assemblies facing awayfrom the focus shield 1620. In one embodiment, the interior surface ofwall 1702 (i.e., the surface of the wall facing the heater element andgetter assemblies) has substantially the same reflectivity as the focusshield.

Other similar embodiments to that shown in FIG. 17 will be apparent tothose of skill in the art. For example, the floor of the L-shield 1703can be omitted so that only wall 1702 is present. Also, the getterassemblies and/or heater element can be supported by means other thansuspension from wall 1702. In one possible embodiment, focus shield 1620can be supported from a second thermally isolating wall substantiallyidentical to, and opposing, wall 1702 to form a "U-shaped" shield. Instill another alternate embodiment, thermally isolating wall 1702 isemployed without focus shield unit 1612 to prevent substantial heatingof the processing chamber outside of the getter pump by heater element1610. In yet another alternate embodiment, heater element 1610 comprisesa reflective coating to direct thermal radiation from the heater elementto the getter material. Such a heater element can be employed inembodiments that lack the above-described focus shield as the reflectivecharacter of the lamps can provide direction of thermal energy from theheater element to the getter material.

One particular alternate embodiment is illustrated in FIG. 18 at 1800.There, a getter pump configuration similar to that illustrated in FIG.17 is shown; but in which getter modules 1802 and 1804 are supported bythermal shield 1806 using supports 1808 and 1810 respectively. A heatingelement 1812 is arranged substantially between the getter modules 1802and 1804 using support 1814. Adjacent the getter pump, at a distance d',is the wall of the processing chamber 1816. The elements are arrangedsuch that reflective interior surface 1818 provides substantialreflection of heat energy from heating element 1812 to getter modules1802 and 1804, while substantially thermally protecting the gettermaterial from other heat sources in the processing chamber. In practice,this embodiment has demonstrated desirable pumping speeds whileproviding good thermal insulating properties to protect both the gettermaterial and other components in the processing chamber. It will beappreciated that the pumping characteristics of the getter pump shown at1800 can be controlled in part by adjusting the distance d' betweenshield 1806 and wall 1816.

Thus, it will be seen that the present invention addresses substantiallythe need to provide an apparatus and method for creating high-vacuumconditions. Using the method and apparatus of the invention as describedherein, high-vacuum states, such as desired in semiconductor processingchambers, can be created more efficiently and effectively thanheretofore possible.

Although the invention has been described with reference to certainexamples and embodiments, it will be appreciated by those of skill inthe art that alternative embodiments can be made which do not departfrom the scope or spirit of the invention. It is therefore intended thatthe following appended claims be interpreted in light of the true spiritand scope of the present invention.

What is claimed:
 1. A getter pump comprising:a thermally isolatingshield having a wall and an open side, said shield having a thermallyreflective inner surface; at least one getter assembly including aplurality of getter elements supported by said wall of said shield andfacing said open side; and a radiant heater supported by said wall ofsaid shield proximate to said at least one getter assembly, wherein saidreflective inner surface of said shield reflects some of the thermalenergy directly radiated by said heating element onto said getterelements.
 2. The getter pump of claim 1, wherein two getter assemblies,each including a plurality of getter elements, are supported by saidwall, and wherein said radiant heater is supported on said wall betweensaid two getter assemblies.
 3. The getter pump of claim 2, furthercomprising a semiconductor processing chamber having a wall, said getterpump being disposed within said chamber such that said wall of saidshield faces said wall of said chamber.
 4. The getter pump of claim 3,wherein said getter pump is disposed a predetermined distance from saidwall of said chamber to obtain a desired pumping speed.
 5. An in-situgetter pump comprising:a) a plurality of getter elements, each of saidgetter elements having an aperture extending there through; b) a meansfor heating said getter material disposed proximate to said gettermaterial; c) a moveable, thermally isolating shield proximate to saidgetter and at least partially surrounding said getter elements; d) achamber enclosing said getter elements, said means for heating and saidthermally isolating shield such that said getter elements are positionedbetween said shield and a wall of said chamber; and e) an inflatabletube coupled with said shield such that when said inflatable tube ischarged with a gas, said shield is moved from said open position to saidclosed position, and when said inflatable tube is discharged said shieldis moved from said closed position to said open position.
 6. A getterpump as recited in claim 5 further comprising gear means coupled to saidshield and said tube for moving said shield between said open and closedpositions when said tube is charged or discharged respectively.
 7. Agetter pump as recited in claim 5 wherein said means for heating saidgetter elements comprises a resistive heating element.
 8. A getter pumpas recited in claim 7 wherein said heating element is disposed throughthe apertures of said getter elements to heat and support said getterelements.
 9. A getter pump as recited in claim 8 wherein said heatingelement is substantially straight for a majority of its length.
 10. Agetter pump as recited in claim 8 wherein said heating element is curvedfor a majority of its length.
 11. A getter pump as recited in claim 5wherein said means for heating comprises a radiative heater.
 12. Agetter pump as recited in claim 5 wherein said getter elements aresubstantially disk shaped members, and wherein said heating element isan elongated, tubular member.
 13. A getter pump as recited in claim 12wherein said getter elements are porous, sintered disks of gettermaterial having a centrally located hub of non-getter material.
 14. Agetter pump as recited in claim 5 wherein said shield comprises areflective surface which faces said getter elements.
 15. A getter pumpas recited in claim 5 wherein said shield is associated with no morethan a 25% conductance loss between said getter elements and anenvironment surrounding said shield.
 16. A getter pump as recited inclaim 5 further including a means for supplying said pump with a noblegas such that when said shield is in a closed position said getterelements are under a positive pressure of said noble gas relative to theatmospheric pressure outside of said getter pump.